hdu5937 Equation

题解其实网上有
突然有点感想
为什么可以用搜索或状压,因为方案数很有限,它要求每种方案不同就意味着搜索的次数也一定,所以现在就应该坚定往这方面想,找部分方案的贪心。这和上一题一样,都是先暴力,后面处理。

#include<bits/stdc++.h>
using namespace std;
#define sz(X) ((int)X.size())
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
typedef long long ll;
const int INF = 0x3f3f3f3f;
const int N = 1e5+5;

int num[15];
int X[15], Y[15], Z[15];
int ans, tmp;
int ok(int x, int nu) {
    if(nu == 0) return 1;
    else if(X[x] == Y[x]) {
        if(num[X[x]] >= 2*nu && num[Z[x]] >= nu) return 1;
    }else if(num[X[x]] >= nu && num[Y[x]] >= nu && num[Z[x]] >= nu) return 1;
    return 0;
}
int cal(){
//  printf("%d: ",tmp); for(int i = 1; i <= 9; ++i) printf("%d ",num[i]);
    int ret = 0;
    int pre[10];
    for(int i = 1; i <= 9; ++i) pre[i] = num[i];
    for(int i = 2; i <= 8; ++i) {
        int mi = min(2, min( num[1], min(num[i], num[i+1]) ) );
        num[1] -= mi; num[i] -= mi; num[i+1] -= mi; ret += mi;
        if(num[1] == 0) break;
    }
    for(int i = 1; i <= 9; ++i) num[i] = pre[i];
    return ret;

}
void dfs(int x, int pr) {
    if(pr) {
        int tt = cal();
        tmp += tt;
        ans = max(tmp, ans);
        tmp -= tt;
    }
    if(x > 13) return;
    int ed;
    if(x < 10) ed = 2; else ed = 1;
    for(int i = 0; i <= ed; ++i) {
        if(ok(x,i)) {
            num[X[x]] -= i; num[Y[x]] -= i; num[Z[x]] -= i; tmp += i;
            dfs(x+1, i);
            num[X[x]] += i; num[Y[x]] += i; num[Z[x]] += i; tmp -= i;
        }
    }
}
int main(){
    int cc = 0;
    for(int i = 2; i <= 9; ++i)
        for(int j = i+1; j <= 9; ++j) {
            if(i+j <= 9) {
                X[++cc] = i; Y[cc] = j; Z[cc] = i+j;
            }
        }
    for(int i = 10; i <= 13; ++i) {
        X[i] = i-9; Y[i] = i-9; Z[i] = Y[i]+X[i];
    }

    int _; scanf("%d",&_);
    for(int cas=1; cas<=_; ++cas) {
        for(int i = 1; i <= 9; ++i) scanf("%d",&num[i]);
        ans = cal(); tmp = 0;
        dfs(1, 0);
        printf("Case #%d: %d
",cas,ans);
    }
    return 0;
}
原文地址:https://www.cnblogs.com/Basasuya/p/8433730.html